Humans have approximately 400 functional olfactory receptors, but among this set there are a large number of variations between individuals. In some cases, these variations cause a receptor to be nonfunctional in a subset of the population. These variations likely underlie inter-individual variation in olfactory perception. Here we propose to identify ligands for odorant receptors, generate a library of odorant receptor variants and determine how responses to odorants are altered in the variants. The data generated in this proposal will be a critical step in our long-term goal to probe olfactory perception in humans by examining the perceptual correlates of these natural receptor variations. These studies lead to the hypothesis that variability in olfactory perception is caused in part by genetic dysfunction of olfactory receptors and that understanding the links between olfactory receptor variation and receptor function will reveal the underlying logic of the human odor code. To test this hypothesis, two specific aims are proposed: Specific Aim 1: Identify ligands for odorant receptors with segregating polymorphisms Specific Aim 2: Characterize the in vitro function and expression of common odorant receptor alleles. The proposed experiments further our long term goals to understand the logic of odor coding in humans.